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libc: add memrchr

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This function scans a string backwards from the end for the first
instance of a character.

Change-Id: I46b21573ed25a0ff222eac340e1e1fb93b040763
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>
This commit is contained in:
Ambroise Vincent 2019-06-19 17:14:09 +01:00 • committed by Olivier Deprez
parent 87b582ef5b
commit ebff107268
3 changed files with 27 additions and 1 deletions
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3
include/lib/libc/string.h
View file

@ -4,7 +4,7 @@
* SPDX-License-Identifier: BSD-3-Clause
*/
/*
* Portions copyright (c) 2018, ARM Limited and Contributors.
* Portions copyright (c) 2018-2019, ARM Limited and Contributors.
* All rights reserved.
*/
@ -23,6 +23,7 @@ int memcmp(const void *s1, const void *s2, size_t len);
int strcmp(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t n);
void *memchr(const void *src, int c, size_t len);
void *memrchr(const void *src, int c, size_t len);
char *strchr(const char *s, int c);
void *memset(void *dst, int val, size_t count);
size_t strlen(const char *s);

1
lib/libc/libc.mk
View file

@ -12,6 +12,7 @@ LIBC_SRCS := $(addprefix lib/libc/, \
memcmp.c \
memcpy.c \
memmove.c \
memrchr.c \
memset.c \
printf.c \
putchar.c \

24
lib/libc/memrchr.c Normal file
View file

@ -0,0 +1,24 @@
/*
* Copyright (c) 2019, Arm Limited. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
#include <string.h>
#undef memrchr
void *memrchr(const void *src, int c, size_t len)
{
const unsigned char *s = src + (len - 1);
while (len--) {
if (*s == (unsigned char)c) {
return (void*) s;
}
s--;
}
return NULL;
}